We are studying how plasma proteins and other large molecules are transported across capillary walls, how they move through the interstitial compartments of tissues and organs, and how they enter the lymph, and are returned to the bloodstream. Our goals are to gain better understanding of the mechanisms by which these processes are brought about, and the relation of protein transport to the control of fluid balance distribution between blood and tissues. Experiments are being carried out on rats, dogs and sheep. The animals are loaded with plasma or protein-free fluids. Samples of blood, lymph and tissues are taken for analysis of protein concentrations and protein distribution. Studies are also being carried out on the transport of proteins through artificial membranes and gels.